1 We can use all present tenses after if, not just the simple present, for example:If she finishes work early, she will go home. (if + simple present + will)If she has finished work by 4 o'clock, she will go home. (if + present perfect + will)

2 We can use all future tenses in the main clauses, not just the will-future:If he doesn't hurry, the plane will have left by the time he gets to the airport.

3 We use Type 1 conditionals to describe what will or won't (probably) happen: If the weather clears, we'll go for a walk. (Not "If the weather will clear")

Write:

Supply the correct forms of the missing verbs.
1 If it (be) fine tomorrow, we (go) for a picnic. see the answer
2 If I (have) time tonight, I (finish) the novel I'm reading. see the answer
3 If it (rain) next weekend, we (not able to) plant the vegetables. see the answer
4 If he (be leaving) at 6 o'clock, I (ask) him to give me a lift. see the answer
5 If she (have drive) all that way since this morning she (be) tired and hungry. see the answer
6 If they (have/be working) all afternoon, they (probably need) a cup of tea. see the answer
7 If I (can't/finish) the job this weekend, I (try) to get it done during the week. see the answer
8 If John (be picked) for the team, he (be boasting) about it for weeks! see the answer
9 If you (have/forget) to phone, they (will have/go) without you. see the answer
10 If we (stay) in this flat till May, we (will have/be living) here for twenty years. see the answer

When we use will in the main clause, we are expressing certainty or near-certainty:
If the weather clears, we'll go for a walk. (certain, or nearly certain)
If we do not feel 'certain' enough to use will, we can use another modal to say what is possible,
necessary or desirable, for example:If it's fine tomorrow, we may go for a swim. (it's possible)If it's fine tomorrow, we must go for a swim. (it's necessary or desirable to do this)

Write:

Supply the correct forms of the missing verbs, but use these modals in the main clause: can, could, may, might, should, ought to, or must. Alternatives are possible.
1 If you (be) still ill tomorrow, you stay at home. see the answer
2 If you (finish) work early, you come for a drink with us. see the answer
3 If she (have) too much to do, she ask someone to help her. see the answer
4 If he (not be coming) tonight, he come next week. see the answer
5 If he (have/only just arrive), he not have heard the news. see the answer
6 If they (have be/waiting) longer than an hour, they be getting impatient. see the answer
7 If we (can't/go) next week, we manage to go the week after. see the answer